Determining battery capacity

Abstract

Methods and related systems conduct a capacity check of a battery via a partial discharge cycle. A method of estimating a total capacity of a battery includes partially discharging the battery at a controlled discharge rate so as to discharge an amount of energy from the battery over a period of time. An output voltage of the battery is measured during the period of time. A total capacity of the battery is estimated based on the amount of energy discharged from the battery during the partial discharge cycle and the output voltage of the battery measured during the partial discharge cycle.

What is claimed is: 
     
       1. A power supply system comprising:
 three power supply units, each of the power supply units comprising a direct current (DC) output connected to an electrical load; and 
 three backup battery units, each of the backup battery units being controllable to output DC power to an associated one of the power supply units at a respective controlled rate; 
 a control unit configured to:
 selectively cause each of the power supply units to draw a constant DC power from the associated backup battery unit during a respective period of time to partially discharge the associated backup battery unit, generate a respective varying DC power from a combination of the constant DC power from the associated backup battery unit and a respective varying AC power from a power source and supply the respective varying DC power to the electrical load; and 
 estimate a respective total capacity of each of the backup battery units based on a total energy discharged by the respective backup battery unit during the respective period of time and output voltage of the respective backup battery unit during the respective period of time. 
 
 
     
     
       2. The power supply system of  claim 1 , wherein the total energy discharged by each of the backup battery units during the respective period of time is less than 50% of the respective estimated total capacity of the backup battery unit. 
     
     
       3. The power supply system of  claim 2 , wherein the total energy discharged by each of the backup battery units during the respective period of time is less than 25% of the respective estimated total capacity of the backup battery unit. 
     
     
       4. The power supply system of  claim 1 , wherein the control unit is further configured to:
 compare, for each of the backup battery units, the estimated total capacity of the backup battery unit with a minimum required total capacity for the backup battery unit; and 
 generate, for one of the backup battery units, an output indicating that the backup battery unit lacks adequate total capacity in response to the estimated total capacity of the backup battery unit being less than the minimum required total capacity for the backup battery unit. 
 
     
     
       5. The power supply system of  claim 1 , wherein the control unit is further configured to:
 determine a total estimated capacity for all of the backup battery units excluding a designated one of the backup battery units; 
 determine if the total estimated capacity for all of the backup battery units excluding the designated one of the backup battery units exceeds a minimum required capacity for conducting a capacity gage calibrating full discharge cycle of the designated one of the backup battery units; and 
 in response to the total estimated capacity for all of the backup battery units excluding the designated one of the backup battery units exceeding the minimum required capacity for conducting the capacity gage calibrating full discharge cycle of the designated one of the backup battery units, control operation of the power supply unit associated with the designated one of the backup battery units to:
 charge the designated one of the backup battery units to a full charge level; 
 discharge the designated one of the backup battery units from the full charge level to an empty charge level; 
 determine an amount of energy discharged by the designated one of the backup battery units during the discharge from the full charge level to the empty charge level; 
 charge the designated one of the backup battery units from the empty charge level to the full charge level; and 
 calibrate a capacity gage of the designated one of the backup battery units based on the amount of energy discharged during the discharge from the full charge level to the empty charge level. 
 
 
     
     
       6. A power supply system comprising:
 a backup battery unit; 
 a power supply unit comprising a direct current (DC) output connected to an electrical load; and 
 a control unit configured to:
 control the power supply unit to draw a controlled DC power from the backup battery unit during a period of time to partially discharge the backup battery unit generate a varying DC power from a combination of the controlled DC power from the backup battery unit and a varying alternating current (AC) power from an AC power source and supply the varying DC power to the electrical load; and 
 estimate a total capacity of the backup battery unit as a function of total energy discharged by the backup battery unit during the period of time and an output voltage of the backup battery unit during the period of time. 
 
 
     
     
       7. The power supply system of  claim 6 , wherein the control unit is configured to terminate discharging of the backup battery unit when the output voltage of the backup battery unit drops to a predetermined voltage that is greater than a minimum useable voltage of the backup battery unit. 
     
     
       8. The power supply system of  claim 6 , wherein the period of time is a predetermined amount of time. 
     
     
       9. The power supply system of  claim 6 , wherein the total energy discharged by the backup battery unit during the period of time is less than 50% of the estimated total capacity of the backup battery unit. 
     
     
       10. The power supply system of  claim 9 , wherein the total energy discharged by the backup battery unit during the period of time is less than 25% of the estimated total capacity of the backup battery unit. 
     
     
       11. The power supply system of  claim 6 , wherein the control unit is further configured to:
 compare the estimated total capacity of the backup battery unit with a minimum required total capacity for the backup battery unit; and 
 generate an output indicating that the backup battery unit lacks adequate total capacity in response to the estimated total capacity of the backup battery unit being less than the minimum required total capacity for the backup battery unit. 
 
     
     
       12. The power supply system of  claim 6 , further comprising:
 a second backup battery unit; and 
 a second power supply unit comprising a second DC output connected to the electrical load, 
 and wherein the control unit is further configured to:
 selectively cause the second power supply unit to draw a second constant DC power from the second backup battery unit during a second period of time to partially discharge the second backup battery unit generate a second varying DC power from a combination of the second constant DC power from the second backup battery unit and a second varying AC power from the AC power source and supply the second varying DC power to the electrical load, the second period of time not overlapping the period of time; and 
 estimate a total capacity of the second backup battery unit based on a total energy discharged by the second backup battery unit during the second period of time and an output voltage of the second backup battery unit during the second period of time. 
 
 
     
     
       13. The power supply system of  claim 12 , further comprising:
 a third backup battery unit; and 
 a third power supply unit, 
 and wherein the control unit is further configured to:
 determine a combined estimated capacity that includes the estimated total capacity of the first backup battery unit and the estimated total capacity of the second backup battery unit; and 
 in response to determining that the combined estimated capacity exceeds a minimum required capacity for conducting a capacity gage calibrating full discharge cycle of the third backup battery unit, control operation of the third power supply assembly to:
 charge the third backup battery unit to a full charge level; 
 discharge the third backup battery unit from the full charge level to an empty charge level; 
 determine an amount of energy discharged by the third backup battery unit during the discharge from the full charge level to the empty charge level; 
 charge the third backup battery unit from the empty charge level to the full charge level; and 
 calibrate a capacity gage of the third backup battery unit based on the amount of energy discharged by the third backup battery unit during the discharge from the full charge level to the empty charge level. 
 
 
 
     
     
       14. A method comprising:
 controlling a power supply unit to:
 draw an amount of electrical energy from a battery over a period of time to partially discharge the battery at a controlled discharge rate, 
 output a varying direct current (DC) power to a load; and 
 generate the varying DC power output to the load by the power supply unit from a combination of the amount of energy drawn from the battery over the period of time and a varying alternating current (AC) power from an AC power source; 
 
 measuring an output voltage of the battery during the period of time; and 
 estimating a total capacity of the battery as a function of the amount of electrical energy and the output voltage. 
 
     
     
       15. The method of  claim 14 , wherein the controlled discharge rate is constant. 
     
     
       16. The method of  claim 15 , wherein the discharging of the battery is terminated when the output voltage of the battery drops to a predetermined voltage that is greater than a minimum useable voltage of the battery. 
     
     
       17. The method of  claim 14 , wherein the period of time is a predetermined amount of time. 
     
     
       18. The method of  claim 14 , wherein the amount of energy discharged by the battery is less than 50% of the estimated total capacity of the battery. 
     
     
       19. The method of  claim 14 , wherein estimating the total capacity of the battery as a function of the amount of energy and the output voltage comprises:
 reading one or more total capacity estimate values from a data lookup table corresponding to the amount of energy and the output voltage; and 
 determining the estimate of the total capacity of the battery based on the one or more total capacity estimate values read from the data lookup table.